This invention relates to friction clutches, particularly for motor vehicles, and provides improved friction material and carrier assemblies for the driven plates of dry plate clutches.
Such clutches present an extremely complex design and production problem because they have to be produced in very large numbers to consistent standards and suit a wide variety of drivers, ranging from strong, experienced and skillful drivers to learners taking their first driving lesson. Every driver will remember the first attempt to achieve clutch control.
In spite of intensive development throughout the history of motor vehicles, with very substantial improvement, there remain problems at the critical point of engagement between the driving member (flywheel) and driven plate. There are three major symptoms of these problems which may occur individually or in various combinations i.e. uneven take-up of the drive, producing vibration known as "judder", local heating of the driven plate friction material producing the phenomenon known as fade and intense local overheating of the driven plate clamping surfaces, on the flywheel and pressure plate respectively, resulting in "heat spots" which spoil the surfaces and cause rapid wear of the friction material and in extreme cases thermal cracking and failure of the pressure plate.
Although the clamping surfaces are produced to very high standards of surface finish and plane configuration and are carefully axially aligned, they are rotatable and essentially relatively axially displaced members so that they cannot in practice have an absolutely constantly parallel, axially spaced relationship in clamping the driven plate.
This means that the driven plate must be made with a capability of conforming to the configuration and attitude of the clamping surfaces and there is a wide variety of driven plate construction intended to achieve this.
There remains however scope for improvement in drive take-up, without judder, and avoidance of heat-spotting to save wear and fade.
The factors involved in clutch construction, operation and control are so complex that systematic study can only be conducted in particular aspects of design, materials and operation and compromises are necessary. To take one example, the values required for optimum take-up and drive transmission between the clamping surfaces and the driven plate are subject to the requirement for practicable clutch pedal movement and operation by a wide variety of drivers, from strong to weak.
Consequently progress depends upon empirical development to establish factors in terms of clutch operation experience rather than absolute values.
The present invention is the result of investigation to find those characteristics of a driven plate which give good results in operation and this has focussed attention on the friction facing material and carrier assembly in its conformation to the clamping surfaces and response to change in axial load in take-up of the drive.